Chapter III

The Historical Source Located

Popper, Kuhn, Lakatos and Feyerabend have succeeded in making
irrationalist philosophy of science acceptable to many readers who would
reject it out of hand if it were presented to them without equivocation and
consistently. It was thus that the question arose to which the first Part of
this book was addressed: namely, how did they achieve this? My answer was,
that they did so principally by means of two literary devices discussed in
Part One. The question to which the present Part of this book is addressed
is: how was irrationalist philosophy of science made acceptable to these
authors themselves?

Some part of the answer to this question no doubt lies in those very
misuses of language which have already been discussed. For there is no reason
to suppose that our authors' characteristic treatment of logical expressions
and success-words has imposed on the writers any less than on their readers.
But obviously, there must be some much more basic answer than this to the
historical question which I have just raised. How did irrationalism about
science come to recommend itself at all and in the first place, to
some leading philosophers from about 1920 onwards, as it did not, and could
not have done, to their counterparts a hundred or two hundred years earlier?
It must be in principle possible to explain this phenomenon, just as it is
possible in principle to explain any other large-scale movement in the
history of thought.

It is not to be assumed, of course, that the origins of recent
irrationalist philosophy of science are purely intellectual: that
this philosophy came into being solely as a result of our authors accepting
some thesis or other, and duly accepting its logical consequences. The
common-sense assumption is in fact the other way. Any large-scale movement of
thought is likely to be brought about, at least in part, by non-intellectual
causes; and the present case is presumably no exception.

Nevertheless it will be taken for granted here that the origins of the
movement of thought with which we are concerned are at any rate
principally intellectual: that is, that the irrationalist
conclusions of our authors' philosophy are embraced by them
principally because they are logical consequences of some premises which
these authors accept. Not to take this for granted would amount to
intolerable condescension towards the authors in question, similar in kind to
that by which Marxist writers `explain' Darwin as though he were some some
simple mechanical toy.

The question is, then, what are the intellectual origins of recent
irrationalism in the philosophy of science? Since we are looking for
intellectual origins, the answer must consist in some
thesis or other. And since were are looking for origins,
the thesis must be one which functions in our authors' philosophy as a
premise, and not as a consequence of other theses. Further still:
what we seek to identify is that one among their premises which is the
key premise of their irrationalism, in the sense that without it their
philosophy of science would not have (that is, the other premises of it do
not have) any irrationalist consequences at all.

Our question, then, is purely historical. The answer to it, however, is
not of historical interest only. It would indeed be extremely interesting, as
a matter of the history of thought, to know what is the key premise, in the
sense just explained, of recent irrationalist philosophy of science. But the
philosophical interest which indirectly attaches to our enquiry is
greater still. What philosophers will want most to know, concerning the key
premise of our authors' philosophy, is whether or not it is true.
But in order for that to be known, it is an obviously indispensable
preliminary, that it be known what this proposition is.

In this book only the preliminary and historical task, of identifying this
proposition, is attempted; not the philosophical task of determining its
truth-value. But if we can do even this much, then there will be some
immediate and substantial benefit to philosophers. Controversies constantly
take place between our authors (or their followers) and other philosophers
who, while they share some of our authors' premises, disagree with
their irrationalist conclusions. If our authors' key premise were once
identified, then it would be known, to both sides in such controversies,
where their disagreements begin. How valuable such information is, in
enabling pointless discussion to be avoided, and yet how hard to come by in
philosophy, no philosopher need be told.

2

Since most of the quotations in Part One illustrated ways in which our
authors' irrationalism is disguised, we should here satisfy
ourselves that the phenomenon which we wish to explain really does exist:
that is, that our authors' philosophy of science really is irrationalist. The
best way to do this with reasonable brevity is to put before the reader (who
is assumed to be familiar with their writings) a few concrete and pungent
reminders of those writings: to cite some things our authors say about
science, which, while they are indisputably representative of their
philosophy, are at the same time extremely and overtly irrationalist. This is
what is done in the present section.

First, then: if there has been a great increase in knowledge in recent
centuries, then a fortiriori there sometimes are such things as
positive good reasons to believe a scientific theory; but Popper says
expressly, repeatedly, and emphatically, that there are not and cannot be
such things. This thesis is so startlingly irrationalist that other
philosophers, as Popper himself tells us, sometimes "cannot quite bring
[themselves] to believe that this is my opinion". But it is: "There
are no such things as good positive reasons" [1] to believe any scientific theory. "Positive reasons
are neither necessary not possible" [2].

These opinions will be admitted to be irrationalist enough: and they are
too deliberately and emphatically expressed to be unrepresentative.

A scientific theory, Popper never tires of reminding his readers, is never
certain in relation to, or in other words deducible from, those propositions
that constitute (in most people's eyes) the reasons to believe it. Of course
I do not cite this as an irrationalist thesis. It is only a
fallibilist one: it asserts no more than the logical
possibility of the conjunction of the evidence for any given scientific
theory, with the negation of that theory. This thesis is so far from being
one which is peculiar to the authors with whom we are concerned, that it is
nowadays a commonplace with almost all philosophers of science. But Popper
goes much further than this. It is a favorite thesis with him that a
scientific theory is, not only never certain, but never even
probable, in relation to the evidence for it [3]. More than that: a scientific theory, he constantly
says, cannot even be more probable, in relation to the empirical
evidence for it, than it is a priori, or in the absence of all
empirical evidence [4].

These two theses will be acknowledged to be irrationalist enough; and they
are ones upon which Popper repeatedly insists. He goes much further still,
however. The truth of any scientific theory or law-statement, he constantly
says, is exactly as improbable, both a priori and in relation to any
possible evidence, as the truth of a self-contradictory proposition [5]; or, to put the matter in plain English (as Popper
does not), it is impossible.

Again: scientific knowledge is usually thought to have at least some
connection with rational belief, but Popper writes: "Belief, of course, is
never rational: it is rational to suspend belief" [6]. One hardly knows what to wonder at more here, the
thesis itself, or the arrogance of the author's "of course". His thesis, as
will be evident, goes far beyond the philosophy of science. But it
certainly does go as far as that, and will be admitted to express, in that
domain, an irrationalism sufficiently uncompromising.

Again: Popper endorses the notorious sceptical thesis of Hume concerning
inductive arguments, or arguments from the observed to the unobserved. This
is the thesis that no proposition about the observed is a reason to believe
any contingent proposition about the unobserved; or in other words, that the
premise of an inductive argument is never a reason to believe its conclusion.
Popper constantly and emphatically, and with detailed references to Hume,
expresses his assent to this thesis. He writes, for example: "I agree with
Hume's opinion that induction is invalid and in no sense justified" [7]. And again: "Are we rationally justified in
reasoning from repeated instances of which we have experience to instances of
which we have had no experience? Hume's unrelenting answer is: No, we
are not justified [...] My own view is that Hume's answer to this problem is
right [...]" [8]. There are many other
statements by Popper to exactly the same effect [9].

Scepticism about induction is an irrationalist thesis itself, but its
irrationalist character is enormously amplified if it is combined, as it is
in Hume and in Popper, with the thesis of empiricism: that is, with the
thesis that no propositions other than propositions about the
observed can be a reason to believe a contingent proposition about the
unobserved. For then it follows at once (since inductive scepticism says that
there can be no reason from experience), that there can be no reason at
all, to believe any contingent propositions about the unobserved: which
class of propositions includes, of course, all scientific theories. Hume,
being an empiricist, did draw from his inductive scepticism this even more
irrationalist conclusion: `scepticism about the unobserved', as we may call
it. And Popper, for the same reason, does the same.

Hume's inductive scepticism, while it is an irrationalist thesis among
others in Popper's philosophy of science, is also more than that: it is one
on which all the others logically depend. Whenever Popper undertakes, as he
often does, to explain the grounds of his philosophy of science, and
especially of whatever is most irrationalist in it, the reader is sure to
meet with yet another of Popper's expositions, with detailed reference to
Hume's writings and with unqualified endorsement of Hume's scepticism about
induction [10]. If we take any other
representative expression of Popper's irrationalism (for example, those
mentioned above in the second to the sixth paragraph of this section), and
ask ourselves "Why does Popper believe this?", then part at least of the
answer is always the same, and always obvious. It is because he shares Hume's
scepticism about induction.

It would be easy to extend indefinitely a list of irrationalist theses
which are representative of our authors; but there is no need to do so here.
The examples given above suffice for the present purpose, which was only to
satisfy ourselves that the philosophy of science here in question really is
irrationalist. It is a sufficient condition for a philosophy of science to be
irrationalist (as we said at the beginning of this book) if consistency with
it requires reluctance to admit that there has been a great increase of
knowledge in recent centuries. Popper's philosophy of science, it will be
evident even from the few samples of it given above, fulfills this condition
amply.

The examples of irrationalist theses given above were not only few in
number, but were all drawn from Popper, none of them from any of our other
three authors. But this too is perfectly proper, and in fact appropriate.
Popper's philosophy of science is at any rate not more irrationalist
than that of Feyerabend, Kuhn, or Lakatos, and at the same time, as a matter
of well-known history, Popper's philosophy owes nothing to theirs, while
Kuhn's philosophy owes much, and the philosophy of Lakatos and Feyerabend
owes nearly everything, to Popper.

3

Our object, then, is to identify the key premise (in the sense explained
earlier) of the reasoning by which our authors have been led to such
irrationalist conclusions about science as have been cited in the preceding
section.

There is no reason to expect this identification to be very easily made.
It is always harder to identify a person's premises than to identify his
conclusions. The reason is obvious. A reasoner's premises or starting-points
are those propositions which he feels most entitled to take for granted. They
are, therefore, the parts of his reasoning which are least likely to be
explicit enough to enable other people to identify them easily. Indeed, it is
sometimes difficult or even impossible for the reasoner himself to
identify all his premises. For a proposition can be a premise of a person's
reasoning without his ever having put it into words, and even without his
being conscious of believing it at all.

It is nowhere of more importance than in philosophy to make clear what our
reasoning is, and hence what our premises are; and most philosophers
accordingly, at least aim to achieve these things. But, whether from
differences in temperament or in training, their actual achievements in this
respect are very unequal, and many philosophers simply are not clear enough
reasoners to enable their premises to be identified with any confidence.
Again, it will be difficult to identify a philosopher's premises, however
clear a reasoner he may be, in proportion as his philosophy is derivative
from some one else's. If, for example, what one philosopher does is
principally just to illustrate a position which he takes to have
been placed beyond dispute by another philosopher, then it will hardly be
possible to discover, from his writings, what the ultimate grounds
are on which that position rests.

For these reasons, it would be idle to try to identify the key premise of
recent irrationalist philosophy of science, from the writings of Lakatos,
Feyerabend, or Kuhn. Lakatos is the only one of these three who is a clear
enough reasoner to hold out any hope of such identification. But it is in
fact impossible in all three, because of the extremely derivative character
of their philosophy. In their writings, irrationalism about scientific
theories functions, not as a conclusion at all, but as a premise, and as an
inexplicit and scarcely-conscious one at that. Of what such irrationalism is
a consequence, it is the least of their concerns to make clear. They
are hardly to be looked to even for the enunciation of general
irrationalist theses about science, such as Popper scatters so freely over
his pages; still less, therefore, are they to be looked to for the arguments
for them. In recent irrationalist philosophy of science, these authors are
fortunate heirs, and like most persons of that kind, they are more
concerned to enjoy their inheritance than to enquire into the grounds of it.
Feyerabend and Kuhn made some slight additions to their irrationalist
inheritance; Lakatos made some trifling abridgements of it, as though he were
slightly uneasy about it; but what all of them chiefly did was simply to
illustrate it, from chosen episodes in the history of science.

Popper on the other hand, writing as he was a generation before these
authors, and for a less enlightened age, was obliged, as they never were, to
work for his irrationalist theses: to argue for them. He it was in
fact, and no one else, who made `straight in the desert a highway' for these
writers, so that irrationalism could thereafter be treated as a settled thing
and a starting-point. It is to Popper, therefore, and to him alone, that we
must look, in our attempt to identify the key premise of recent
irrationalism. But since he is also a clearer reasoner than any of our other
authors, we can do so with some prospect of success.

In such theses as those of Popper which were mentioned in the preceding
section, there is nothing new. What were there cited as
representative expressions of new irrationalism, could equally be cited as
representative expressions of old scepticism. That it is always rational to
suspend belief, is a thesis of Pyrrho as well as of Popper: that from what
has been experienced, nothing can be rationally inferred about what has not,
is a thesis of Hume as well as of Popper; and so on. It is new, of
course, to have such sceptical or irrationalist theses as these filling huge
books called "The Growth of Scientific Knowledge" [11], "The Logic of Scientific Discovery", etc., etc.
But then (as was said at the beginning of the book), when it is obvious that
knowledge has increased, authors who wish to imply the opposite and yet
retain plausibility must write in ways apt to mislead their readers.
But in the substance, as distinct from the literary form, of Popper's
philosophy, nothing is new. In particular, Popper himself makes clear (as I
have said), that the scepticism of Hume about inductive arguments is not only
one of his own irrationalist theses, but part of the immediate grounds of all
the others.

In this dependence of Hume, Popper is only an extreme case of a general
condition. For the influence of Hume on 20th-century philosophy of science in
general is in fact so great that it is scarcely possible to exaggerate it. He
looms like a colossus over both of the main tendencies in philosophy of
science in the present century: the logical positivist one, and the
irrationalist one. His empiricism, his insistence on the fallibility of
induction, and on the thesis which follows from those two, of the permanent
possibility of the falsity of any scientific theory, are fundamental planks
in the platform of both of these schools of thought. Where the two schools
separate is that the irrationalists further accept, while the logical
positivists reject, Hume's further, sceptical, thesis about
induction: that the premise of an inductive argument is no reason to believe
its conclusion. This is why the logical positivists, in the 1940's and '50's
set about constructing what they called `confirmation-theory', `non-deductive
logic', `the theory of logical probability', or `inductive logic': a branch
of logic which, while being consistent with empiricism and inductive
fallibilism, would allow scientific theories to be objects of rational belief
without being certain. The irrationalists, on the other hand, being
Humean sceptics and not merely fallibilists about induction, deny the
possibility of any such theory; and Popper, accordingly, makes the chief
landmark of `inductive logic', Carnap's Logical Foundations of
Probability, a principal target of his criticism [12].

In the sharpest possible contrast to all this, the influence of Hume on
philosophy of science in the 19th century was but slight. For this
extraordinary reversal in the importance attached to Hume's philosophy of
science, the historical reason is obvious enough, at least in broad terms.
The crucial event was that one which for almost two hundred years had been
felt to be impossible, but which nevertheless took place near the start of
this century: the fall of the Newtonian empire in physics. This catastrophe,
and the period of extreme turbulence in physics it inaugurated, changed the
entire climate of philosophy of science. Almost all philosophers of the 18th
and 19th centuries, it was now clear, has enormously exaggerated the
certainty and the extent of scientific knowledge. What was needed, evidently,
was a far less optimistic philosophy of science, a rigorously
fallibilist philosophy, which would ensure that such fearful
hubris as had been incurred in connection with Newtonian physics
should never be incurred again. Well, the very thing needed was lying at
hand, though long neglected; and Hume, 150 years after his death, finally and
fully came into his own.

Thus the revival of Hume's philosophy of science in this century was a
movement of retreat from that confidence in science which was so high, and
constantly rising, in the two preceding centuries, and which had proved to be
misplaced precisely where it was highest. This retreat was general, all
empiricist philosophers taking part in it. Popper and his followers are
simply those with whom the retreat turned into a rout. They fell
back all the way to Hume: not just to his fallibilism but to his
scepticism about induction; and hence (since they were empiricists)
to his scepticism in general about the unobserved.

Their only object was, and has remained, to ensure that no scientific
theory should ever again become the object of over-confident belief; since
only in that way can it be guaranteed that such a fall as overtook Newtonian
pride will never be repeated. Now, it was the belief that a scientific theory
can be certain, which had made that fall possible. So it must be
re-affirmed, with Hume, that a scientific theory is never deducible
from the observational evidence for it. On this negative logical Popper
and his followers accordingly insist, and insist ad nauseum, even
though no empiricist any longer dreams of denying it. They insist on it to
the exclusion of every other logical relation which might exist between a
scientific theory and the evidence for it, and they deny, with Hume, that
propositions about the observed can ever be a positive reason to believe a
scientific theory. They must do so: otherwise, it might one day happen that a
scientific theory should again be mistaken for a certainty. And that, for
these philosophers, is what must at any cost be prevented.

This same consuming anxiety, it is worthwhile to point out, finds
expression even in the very germ of Popper's philosophy: that is, in his
opinions as to what constitutes a scientific theory, and what makes
one such theory better than another. The very mark of a scientific theory, he
thinks, is that it should be able to be disproved by experience
[13]; and one scientific theory is better
than another (other things being equal), he thinks, if it is more
disprovable than the other [14]. No opinions
could express more poignantly than these the depth of Popper's dread lest
Newtonian hubris should ever have a sequel. For this is to say that
the very mark of a scientific theory is that it be possible for us to
repel any claims it might have on our belief, and that a theory is
the better, the more easily the burden of belief which it threatens
to impose on us can be put off. And nothing, evidently, could have suggested
so strangely inverted a conception of science, except the most intense
recollection of the traumatic consequences of having once fully believed a
false theory.

Such is the genesis of Popper's philosophy of science. It is a story of
one kind of reaction to the disappointment of extreme expectations: that kind
of reaction, namely, of which the best epitome is given in Aesop's fable of
the fox and the grapes. The parallel would be complete if the fox, having
become convinced that neither he nor anyone else could ever succeed in
tasting grapes, should nevertheless write many long books on the progress of
viticulture.

We have made a beginning, then, in our attempt to identify the key premise
of recent irrationalist philosophy of science. That premise is to be looked
for, among our authors, in Popper and nowhere else. The irrationalism of
Popper about scientific theories has turned out to be no other than the
scepticism of Hume concerning contingent propositions about the unobserved.
We know what are the immediate grounds, both in Hume and in Popper, of that
irrationalism or scepticism: the conjunction of the theses of empiricism and
inductive scepticism.

It is obvious, furthermore, which of these two immediate grounds is the
key to the irrationalism of this consequences to their conjunction.
It is the thesis of inductive scepticism. From the empiricist ground on its
own no irrationalist consequence follows.

But all this is only a beginning, since what we have so far identified are
only the immediate grounds of Popper's irrationalism concerning scientific
theories. What we want to know, however, are the ultimate grounds of it. At
least, we want to know that ultimate ground without which his philosophy of
science would have no irrationalist implications.

The thesis of inductive scepticism cannot possibly be itself that
ultimate ground or premise of Popper's irrationalism. It operates as a tacit
premise, indeed, in the philosophy of Feyerabend, Kuhn, and Lakatos; but
then, that is just the principal respect in which these philosophers are
careless beneficiaries of Popper's labors. At no earlier period than theirs
in the entire history of philosophy could a respected philosopher (not to say
a sane man) have started from the assumption that the observed can
furnish no reason to believe anything about the unobserved. Certainly Popper,
writing in an earlier and less enlightened age, had to have some
argument for so startlingly irrationalist a thesis.

Our search for the key premise of our authors' irrationalism leads us,
then, to the question: what are the premises of Popper's argument for
scepticism about induction? How was inductive scepticism itself
established?

Just as in general our other authors are derivative thinkers in relation
to Popper, so Popper in turn, here at any rate, is a derivative thinker in
relation to Hume. Indeed, on this all-important matter of the grounds of
inductive scepticism, he is entirely so. Popper's argument for scepticism
about induction is simply Hume's argument for it. He has neither fault to
find with Hume's reasoning for this conclusion, nor anything to add to it. "I
regard Hume's formulation and treatment of the logical problem of induction
[...] a flawless gem" [15]. What Hume gave
us, Popper says, is "a gem of priceless value [...]: a simple,
straightforward, logical refutation of any claim that induction could be a
valid argument, or a justifiable way of reasoning" [16].

This being so, we know at any rate this much about the key premise of
Popper's argument for inductive scepticism: that it is the key premise,
whatever that is, of Hume's argument for the same conclusion. For these
arguments are one and the same.

The reader of Popper is naturally led to expect, by such passages as have
just been quoted, that he is about to be told what this perfect and simple
argument of Hume's was. But the reader is disappointed in this expectation.
Hume's conclusion is there stated and endorsed by Popper, but his argument
for it is only praised, not stated. There are, however, other places in his
writings where he does attempt to say what Hume's argument was [17]. These accounts differ widely in how much of the
detail of Hume's argument they disclose. Some of them are mere hints of the
argument, too brief or obscure to make any of its internal structure visible
at all [18]. In other cases Popper's account
does succeed in making some of the structure of Hume's argument clear
[19]. For our purposes, however, what is
required is an account of Hume's argument which enables us to identify its
premises, and all of them. From this point of view all
Popper's accounts of Hume's argument are extremely deficient. It would be
only with the greatest difficulty, if at all, that anyone could learn from
Popper what even one of Hume's premises was.

It should not surprise us that Popper has reproduced only very
incompletely the argument which he praises so lavishly. On the contrary, this
was to be expected. It is simply another instance of the obvious rule which
was stated earlier: that the more derivative a thinker is in relation to
another, that is, the more he regards that other as having placed a certain
conclusion beyond dispute, the less likely he is to make clear what the
original grounds were on which that conclusion rested.

The deficiencies of Popper's account of Hume's argument do not, however,
impose any obstacle to our enquiry. They are simply an additional reason why
the historical focus of that enquiry must now go back beyond Popper. We must
simply identify that premise of Hume's argument for inductive
scepticism, without which it would not have its irrationalist conclusion. The
fact that Popper's accounts of that argument are very imperfect, does not
matter at all. Had he given ever so good an account of it, still, since the
argument in question, by Popper's own testimony, is Hume's, it is Hume's
argument to which we ought to turn our attention.

The shift of the focus of our enquiry back to Hume, while it is in any
case necessary, is also attended by marked advantages. For one thing, Hume is
a clearer reasoner than any of our four modern authors. Secondly, and even
more important, the circumstances in which Hume argued for inductive
scepticism were much more conducive to explicitness of argument on this point
than those in which Popper did. Popper did so in a period of catastrophic
collapse of confidence in science (as well as of confidence in much else)
[20], a period in which irrationalist theses,
such as inductive scepticism, were greedily embraced by many of his readers
almost faster than Popper could write them down. Hume, living in a less
enlightened age, had no such assistance. On the contrary, he had to argue for
scepticism about induction, not only from a standing start (as it were), but
entirely against the prevailing current of opinion. The current of
Newtonian confidence, in particular, was already then so strong as to be
irresistible except by the hardiest of sceptics. Popper, therefore, even if
his native talent for clear reasoning had been as great as Hume's, was bound
to be, on this subject, the less explicit reasoner of the two.

That Hume's philosophy of science is the source of a great deal of
subsequent irrationalism, has been, of course, widely recognized: for
example, by Bertrand Russell [21]. Indeed, it
is emphasised by Popper himself [22]. Popper
does not admit, of course, that his own philosophy of science is
irrationalist, but it is as obvious to him as it is to everyone else that
Hume's is [23], and he has been admirably
explicit (as we have seen) in acknowledging the debt he owes to Hume.

In this respect our other authors compare very unfavorably with Popper.
Their debt to Hume's philosophy (which means in the end, as we have seen,
their debt to his sceptical thesis about induction) is not less than
Popper's; it is only less direct. Yet one would look in vain in their
writings for any direct, indeed almost for any indirect, acknowledgment of
this indebtedness. Indeed, one has only to recall the thesis to which they
are indebted (namely, the premise of an inductive argument is no reason to
believe its conclusion), to see at once how utterly out of place it would
have been for these authors even to mention it. Popper had made Humean
scepticism about induction so much de rigueur, that even to affirm
it had become extremely unfashionable; almost as much so, indeed, as to deny
it. For the author of The Structure of Scientific Revolutions, or of
The Methodology of Scientific Research Programmes, to introduce this
simple old thesis into their works, would have been felt as an
intolerable piece of rusticity. The proprietor of a pornographic book shop
may be dimly conscious of a debt to the author of Areopagitica, but
Milton is the last person he wants to see in his shop.

In later works, however, there are two small and indirect indications that
these authors do after all recognize, in this homely thesis of Hume,
the progenitor of their own irrationalism.

Lakatos' philosophy of science was no sooner published than it was
outflanked on the left (so to speak) by the still more irrationalist
philosophy of his friend Feyerabend. Thus by a manoeuvre not the less amusing
for being familiar, Lakatos found himself placed, late in his life, in the
unaccustomed role of defender of science, against
neo-Popperian irrationalism. In this extremity (we are told by Feyerabend,
who is here referring mainly to unpublished discussions between them),
Lakatos was reduced to objecting that even irrationalist philosophers do not
"walk out of the window of a 50-story building instead of using the lift"
[24]. Feyerabend admits he was baffled by
this objection "for quite a while"; as anyone might have been, by an
objection so extremely recherche. Finally, however, he found a reply
which the irrationalist can make to it, and he gravely explains what it is.
This reply is fully as original as the objection, and is in fact, though
apparently all-unknowingly, pure Hume. It does not matter, Feyerabend tells
us, what he or anyone else "does or does not do", or feel, about walking out
of high windows; what matters is that neither he nor anyone else "can give
reasons for his fear" of doing so [25].

Kuhn provides a less picturesque but equally clear belated acknowledgment
of the central part played in his philosophy of science by scepticism about
induction. In an article first published in 1977, he tells us that, if he
finds himself unable to avoid certain views of science which some people
regard as irrationalist, "that is only another way of saying that I make no
claim to have solved the problem of induction" [26].

The ordinary philosopher comes across these two passages with mingled
relief, astonishment, and indignation. Relief, because what he had privately
believed all along, he now finds indirectly admitted, and admitted by the
emperors themselves: that they have no clothes at all, except such as are
woven out of Hume's scepticism about induction. Astonishment and indignation,
because previously and apart from these two passages, nothing in these
authors had prepared him for such an admission, and everything had in fact
pointed the other way. There is not one word in Kuhn's The
Structure of Scientific Revolutions from which a reader could infer that
Kuhn believes that a problem of induction exists; much less infer that he
believes it to have something to do with his philosophy of science. As for
the debate about the rationality of believing one can safely walk out of high
windows: what is this `pastoral-comical' scene, in which Lakatos plays
Beattie to Feyerabend's Hume, but an admission that what is principally at
stake between irrationalists and their critics is the sceptical thesis of
Hume about the possibility of learning from experience? A thesis which was
old when Sextus Empiricus wrote, and which requires for its discussion
examples no more esoteric than Hume's own about walking out of windows
[27], or the one always associated with
Pyrrho, of walking over cliffs [28]! "But
until now", the indignant reader exclaims, "these authors had led me to
believe that, before I could enter the lists against their philosophy of
science, I would have to have read at least as much as they have written
about Galileo and the telescope, about Lavoisier and oxygen, about the
Bohr-Kramers-Slater theory, about the Lummer-Pringsheim experiments, etc.,
etc. What! Was all of this really quite inessential all along? Was it
bestowed on me, then principally, ad terrorum?" Alas, poor reader,
it was.

However belated or infrequent their own acknowledgment of it, then, the
philosophy of these authors depends, no less critically than the philosophy
of Popper does, on the scepticism of Hume about induction. This historical
fact has some extremely curious corollaries. For example, that had it not
been for the author of the most famous of all attacks on the credibility of
miracles, the author of Against Method would not have believed a
vulgar charlatan who claimed to become a raven from time to time [29]. But it is in any case a fact, and we must now
turn to the argument of Hume on which this all-important thesis of
irrationalist philosophy rests. For the key premise, whatever it is, of
Hume's argument for inductive scepticism, is also the key to our whole
enquiry.